The present invention relates to a method for cutting a window in a vertical sheet of material, especially sheet metal.
More precisely, the invention relates to the operation of cuttingxe2x80x94by means of a laser, for examplexe2x80x94sheets held in a vertical plane.
A plant for cutting and bending pieces of sheet metal in which the sheets are cut in a vertical plane is described in the Italian patent application No. T095A000569 in the name of the present applicant. As compared with cutting operations in which the metal sheet is held in a horizontal plane, cutting in a vertical plane is associated with the advantage that the plant comes to occupy a smaller floor space and that the equipment needed to support the work piece is simplified. Nevertheless, cutting sheets of sheet metal while held in a vertical plane brings with it a series of problems that are not encountered in the more traditional case in which the sheet to be cut rests on a horizontal table.
One of these problems occurs in the case in which windows have to be cut in metal sheets held in a vertical plane. Hereinafter, in both the description and the claims, the term xe2x80x9cwindowxe2x80x9d is intended to refer to any aperture passing through the sheet, no matter what its shape. Cutting a window inevitably entails the production of a piece of waste material. When the metal sheets are held in a vertical plane, these pieces of waste material can interfere with the cutting process. In fact, these pieces of waste material could fall towards the laser cutting head and thus become entangled with it or cause damage; alternately, they could remain on the sheet to be cut and protrude in the direction of the cutting head, which is particularly liable to happen in the case of sheet metal of considerable thickness, once again becoming entangled with the laser head or causing damage to It. These risks become considerably greater when the pieces of waste material have a generally concave form or parts that either protrude or are recessed, because this will considerably increase the possibility of the piece of waste material becoming entangled with the work piece at the end of the cut of the window.
The present invention has been achieved with such a point in mind. Therefore, the object of the present Invention is to provide a method for cutting a window in a vertical sheet of material, especially sheet metal which overcome s the said problems and drawbacks.
According to the present invention, the object as aforesaid is attained by a method having the characteristics set out in the claims attached hereto.
The innovative concept on which the present invention is based consists essentially of defining a cutting run that returns to its starting point, the said starting point being situated above a horizontal axis passing through the barycentre of the piece of waste material.
Thanks to this solution idea, the pieces of waste material will fall on the side of the metal sheet opposite to the side on which the laser cutting head is being operated, this by virtue of the well known fact that the laser beam is accompanied by a gas jet at a relatively high pressure.
The point at which the cutting run commences and closes is preferably situated above a horizontal axis through the barycentre an d in the vicinity of a vertical axis through that centre, because this will facilitate the piece of waste falling without performing a turning motion.
In the case in which the window to be cut is either of a concave shape or has parts that either protrude or are recessed, the cutting of the window is subdivided in such a way as to cut several pieces of waste material that are devoid of both protrusions and recesses. Each of the pieces of waste material is cut as previously described, that is to say, with a cutting run that closes at its starting point, this point being situated above a horizontal axis through the barycentre and, preferably, also in the vicinity of the vertical axis through the barycentre of the piece of waste material.